This invention relates to valves.
To provide sealing when completely closed, a conventional valve has such a diaphragm on a valve closure member that will flex itself to press upon a seat mounted on a valve housing, the flexion being effected counter to fluid pressure, by an elastic retaining force of the diaphragm. However, a great retaining force is needed to assure a reliable sealing upon closure of the valve. It follows that a great operational force is required for closing the valve to allow the flexion of the diaphragm on the valve closure member. Such has been a disadvantage of the known valve.